During the transfer of a volatile liquid, such as gasoline from a storage facility, there may be an unsealed connection between the disconnectable nozzle and the tank being filled. As the transfer operation progresses, residual gases, as well as air contained within the tank, are sometimes displaced into the atmosphere.
Many municipalities and governmental agencies have proposed or adopted regulations intended to reduce or at least to control these emissions. One method toward complying with mandated regulations is the provision of a substantially, or completely closed system between the fuel source or storage facility and the tank or tanks being filled.
Such a closed system, as found for example at a service station, normally includes individual conduits which carry the vaporizable fuel. The remote end of each conduit is provided with a manually operated dispensing nozzle. The respective nozzles are adapted to be removably positioned within the filler pipe of a receiving tank. Further, the respective nozzles include means to form a partial and preferably a sealed engagement between the nozzle spout and the tank filler tube.
Also, in some instances the fuel carrying system is not fully closed, but rather is controllably vented to the atmosphere. With such an arrangement, as liquid is pumped from the source, either of two eventualities could occur. If fuel leaving the storage tank or source is not immediately replaced by vapor from the tank being filled, air will be drawn into the system. On the other hand, when excessive vapors are withdrawn from the tank being filled, vapors will have to be vented to avoid a pressure build-up.
Several embodiments of sealing arrangements have been found to be advantageous for providing the necessary partial or substantially vapor tight, yet disconnectable engagement with a receiving tank spout. One method for providing the desired engagement is to attach a cylindrical, flexible walled member such as a rubber boot or the like to each fuel dispensing nozzle.
The boot, when properly positioned, will substantially surround the nozzle spout while the latter is registered in place. By use of such an arrangement, when the nozzle is registered within a filler pipe of the receiving tank the walls of the flexible boot will be deflected and/or distorted. The boot will thereby define an annular vapor tight or substantially vapor tight passage.
This type of arrangement is generally found to be highly effective. Thus, when a fuel flow is introduced from a nozzle into a particular receiving tank, a slight pressure is produced within the tank to displace a mixture of air and fuel vapors. The displaced vapors will be urged through the annulus defined by the nozzle spout and the flexible member. The vapors are then conducted by way of the dispensing nozzle through a separate conduit to the fuel source. An alternate holding means for retaining the vapors can be provided rather than in the fuel storage tank.
The effectiveness of this system depends to a large degree on the compatability of the vehicle fuel tank with the nozzle. However, some care must be exercised by an operator to assure a satisfactory engaging relationship at the mating surfaces. If for any reason the contact edges of the nozzle boot do not engage the filler pipe, an imperfect seal arrangement is achieved and vapor leakage can occur.
In conjunction with the most efficient use of closed fuel systems, vacuum assist means have been devised which cause the vapor collection system to operate under a slight vacuum. Operationally, the vacuum system will function to establish a reduced pressure at the nozzle-tank filler pipe juncture, whereby to collect displaced vapor by aspiration.
With a vacuum assist arrangement incorporated into the fuel system a varying degree of vapor to liquid ratio, hereafter referred to as V/L, will be realized depending on the type of nozzle used. For example, with a relatively tight sealing nozzle at the fuel tank, a typical range of V/L ratios can extend from about 0.7 to 1.5. With a non-sealing nozzle, however, the maximum V/L will be somewhat less.
In any event, maintenance of a favorable V/L ratio will avoid ingesting excessive amounts of air which would tend to absorb hydrocarbons in the underground storage tank. The latter condition would result of course in emissions from the tank vent.
A typical range of V/L values with a non-sealing nozzle could extend from about 0.7 to 1.1. It is appreciated that these ranges are expressed as typical values rather than absolute values. In actual practice they could be greater or less depending on the adjustment and control of the dispensing system parameters.
It is therefore an object of the present invention to provide a simple fuel dispensing system which will minimize the quantity of hydrocarbon vapors which are passed to the atmosphere. A further object is to provide a vacuum assist arrangement within the fuel system which will cause the system to function at its maximum efficiency. A still further object is to provide a fuel dispensing system which concurrently regulates the inflow of liquid fuel, to the outflow of vapor, whereby to establish a favorable vapor:liquid ratio.
Toward achieving these objectives the present system overcomes or at least minimizes the potentially detrimental effects of a leak path at the nozzle-tank filler pipe juncture. There is thus provided means to regulate the liquid fuel flow which is discharged from the dispenser such that said flow is maintained within a predetermined range and not in excess of a maximum value. This is achieved through the facility of a suitable liquid flow regulator means which is connected in conjunction with the storage fuel tank, and more preferably with the dispensing mechanism.
Further, vapor throttling means such as a constriction or an orifice is formed in the vapor line. This constriction is at a location where it will affect the vapor flow discharged through the receiving tank; said vapor flow is also affected by the vacuum established through the vacuum assist arrangement.